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Engaging deck causes engine to bog

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Daniel Stroup

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Jul 14, 2021
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Cross Junction, VA
New here. model 3225, 50” deck, shaft drive:
While mowing lawn, the deck suddenly locked up and caused the belts to start smoking and shortly afterwards killed the engine, while I was trying to disengage the clutch.
there was nothing in the blades or belts, by hand the mower deck spins freely, no grinding, no odd noises.
checked PTO belts and everything moves freely. Unengaged engine runs strong. Engage clutch, immediately goes into lock down, slowing engine and starts to smell like burning belt, although not seeing smoke.
wondering if the “Deck transmission” ? Can cause a problem like this. ?
Are there Other possibilities I’m overlooking?
 

dropte

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David Ropte
Does everything turn freely when you turn the shaft by hand?

Is everything ok if you engage it with the PTO shaft disconnected?

I'd lean towards it being a gearbox problem with the deck, though, if it just simply locked up. That machine should have enough juice to smoke the deck belt if it was a spindle or idler pulley on the deck.
 

Daniel Stroup

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Messages
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Location
Cross Junction, VA
Thanks for the reply. I will double check with the deck removed from the mower, blades and belt spun easily.
the engine also spun the forward half of the shaft when disconnected from the deck shaft.
which would pretty well exclude everything except the gearbox.
will let you know.
 

dropte

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You don't have to pull the deck off, just disconnect the PTO shaft to check, but if the problem is in the gearbox, you're going to be pulling the deck anyway.

Did the shaft move when you spun the blades/belt? I'm kinda curious what could have seized up in there if that's what the problem is.
 

Daniel Stroup

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Cross Junction, VA
Hopefully this will make sense to you. I’ve attached a video of me turning the deck by hand. Everything turns with minimal resistance. The engine and PTO shaft turn easily w/o the deck engaged
 

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dropte

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Boy that sure seems ok to me. That's a 44" deck for sure. How easily does the PTO Idler on the tensioner spin? And how easy does the PTO shaft under the tractor spin? There's only the belt on the deck and the two belts that go from the engine to the jackshaft.

It's odd to me that it just locked up. The PTO on the engine is literally just a keyed twin stack of pulleys and no moving parts.
 

Daniel Stroup

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Location
Cross Junction, VA
The engine seems to be running well, I can try again tomorrow with the PTO.
I had rotator cuff surgery last week so I can only do a little at a time with it.
I removed the gear box cover, and everything seems good there.
Maybe there iS a bad bearing at the engine PTO attachment
 

dropte

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Well there's no bearing on the engine, aside from the crank bearings and those certainly aren't seized. There should be an idler pulley that the vacuum actuator presses against the belt, but that locking up wouldn't stop the belts from spinning the deck.

The most likely place is in the PTO jackshaft under the frame. That assembly is also what the axle pivots on IIRC. There are two bearings in that assembly that spin and if one of those seized up it would do what you're describing I would think. You should be able to tell by disconnecting the deck and just spinning that splined shaft and listening/feeling for excessive noise and play. #21 and #22 in the attached image
1627687563528.png
 

Daniel Stroup

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Cross Junction, VA
Thank you for the reply and diagram. When I take a look at it , I suspect you are right XO about the Jack shaft bearing on the frame.
nit is only likely candidate left
The driveshaft universal joints for the deck Flex easily. Eliminating them as well
Will reply back when I have an answer
 

dropte

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It appears to be the Jack shaft bearing. If I rotate the pulley by hand in the direction of engine rotation, it locks up. Reverse rotation it unlocks.
thank you for the help
It’s not supposed to be a sprag :D but hopefully not too awful to swap out.
 
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